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  1. Percona Server for MongoDB
  2. PSMDB-178

upstream has changed SnapshotManager's semantics in 3.6.0-rc0

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    Details

    • Type: Bug
    • Status: Done
    • Priority: Medium
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: None
    • Labels:
      None

      Description

      Due to the changes in wiredTiger's snapshot manager and changes in corresponding unittests some tests are failing for mongo-rocks with "std::exception: _Map_base::at" string in error message.
      Affected tests (list is probably incomplete):

      • storage_rocks_engine_test/SnapshotManagerTests/BasicFunctionality
      • storage_rocks_engine_test/SnapshotManagerTests/FailsAfterDropAllSnapshotsWhileYielded
      • storage_rocks_engine_test/SnapshotManagerTests/UpdateAndDelete
      • no_passthrough_rocksdb.jstests/noPassthrough/change_stream_feature_compatibility_version.js
      • no_passthrough_rocksdb.jstests/noPassthrough/change_streams_require_majority_read_concern.js
      • no_passthrough_rocksdb.jstests/noPassthrough/read_majority.js
      • no_passthrough_rocksdb.jstests/noPassthrough/read_majority_reads.js

      More details:
      BasicFunctionality test fails on the first ASSERT
      because itCountOn() creates cursor
      then in cursor's constructor it tries to get sequence number from the current snapshot
      but _snapshots and _snapshotMap in RocksSnapshotManger are empty
      because RocksSnapshotManager::createSnapshot was deleted in r3.6.0-rc0 (https://github.com/mongodb/mongo/commit/7ef892d32c)
      In other words since createSnapshot was deleted RocksSnapshotManager never contains any snapshots and this causes exception on cursor creation.
      Another thing to check is why we need sequence number in cursor - probably we will eliminate this as part of this issue fix.

        Attachments

        1. MongoDB_RocksDB5.png
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        5. MongoDB_RocksDB.png
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        6. MongoDB_Overview.png
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        7. hang.txt
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        8. Grafana_-_System_Overview3.png
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        11. Grafana_-_MongoDB_RocksDB5.png
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        15. Grafana_-_MongoDB_RocksDB.png
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        16. Grafana_-_MongoDB_ReplSet3.png
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        18. Grafana_-_MongoDB_ReplSet.png
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        19. Grafana_-_MongoDB_Overview2.png
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        20. Grafana_-_MongoDB_Overview.png
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        21. backtrace.log
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              Assignee:
              Unassigned
              Reporter:
              igor.solodovnikov Igor Solodovnikov
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                Updated:
                Resolved:

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